The incorporation into polymer matrices of PCM materials such as fatty acids, salts or paraffins, especially, to release or absorb heat by a change of state by means of the latent heat of fusion which characterizes these PCMs, has been known for a long time. Specifically, these PCMs have the advantage of passing from the liquid state to the solid state while releasing heat during their crystallization, and conversely of passing from the solid state to the liquid state while absorbing heat during their melting. It is known practice to use these PCMs in powder form with nodules dispersed in a thermoplastic or elastomer matrix, or by encapsulating them in microspheres, for example plastic microspheres, or alternatively by grafting them onto a support, in a nonlimiting manner.
Document U.S. Pat. No. 4,617,332 teaches in example 3 thereof the preparation of a crosslinked rubber composition based on an EPDM in which is dispersed in powder form a PCM of paraffin wax type in an amount ranging from 33 to 66 phr only (phr: parts by weight per one hundred parts of elastomer). A major drawback of this composition lies in its relatively low content of PCM, which does not give it a sufficient change of state mass enthalpy MI in order to absorb and restitute the heat energy necessary to control the temperature of a fluid transported by a pipe.
Document EP-A 1-0 412 021 teaches the mixing in the melt state of amounts greater than or equal to 500 phr of a paraffinic PCM in powder form with a polymeric binder consisting of an EPDM, to obtain crosslinked compositions in which the PCM is not in the dispersed phase state but in the continuous phase state, due to its excessively high content in these compositions and to mixing and crosslinking temperatures above 100° C. which bring about a phase inversion.
As a result of this phase inversion, these PCM-based compositions do not have the flexibility and elasticity mechanical properties required to be used in multilayer hoses subjected to large operating deformations.